Two-Electron-Induced Reorganization of Cobalt Coordination and Metal-Ligand Cooperative Redox Shifting Co(I) Reactivity toward CO2 Reduction
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Updated: Aug 13, 2025
Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction
Published on: April 10, 2018
Seungjin Song1,2, Wonjung Lee1,2, Youngseob Lee3
1Department of Chemistry, Gwangju Institute of Science and Technology; Gwangju61005, Republic of Korea.
Abstract:
Electrochemical reorganization of complex structures is directly related to catalytic reactivity; thus, the geometric changes of catalysts induced by electron transfer should be considered to scrutinize the reaction mechanism. Herein, we studied electron-induced reorganization patterns of six-coordinate Co complexes with neutral N-donor ligands. Upon two-electron transfer into a Co center enclosed within a bulky π-acceptor ligand, the catalytic site exhibited different reorganization patterns depending on the ligand characteristics. While a bipyridyl ligand released Co-bound solvent (CH3CN) to open a reaction site, a phenanthroline ligand caused Co-Narm (side "arm" of NNN-ligand) bond dissociation. The first electron transfer occurred in the Co(II/I) reduction step and the second electron entered the bulky π-acceptor, of which redox steps were assigned from cyclic voltammograms, magnetic moment measurements, and DFT calculations. In comparison, the Co complex of [NNNNCH-Co(CH3CN)3](PF6)2 ([1-(CHCN)](PF6)2) showed a high H2 evolution reactivity (HER), whereas a series of Co complexes with bulky π-acceptors such as [NNNNCH-Co(L)(CH3CN)](PF6)2 (L = phen ([2-CHCN](PF6)2), bpy ([3-CHCN](PF6)2), [NNNNCH-Co(tpy)](PF6)2 ([4](PF6)2), and [NNNCH-Co(phen)(CH3CN)](PF6)2 ([5-CHCN](PF6)2)) suppressed the HER but rather enhanced the CO2 reduction reaction. The metal-ligand cooperative redox steps enabled the shift of Co(I) reactivity toward CO2 reduction. Additionally, the amine pendant attached to the NNNNCH-ligand could stabilize the CO2 reduction intermediate through the hydrogen-bonding interaction with the Co-CO2H adduct.
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